Sensor and guide wire assemblies in which a sensor is mounted at the distal end of a guide wire are known. In U.S. Pat. No. Re. 35,648, which is assigned to the present assignee, an example of such a sensor and guide wire assembly is disclosed, where a sensor guide comprises a sensor element, an electronic unit, a signal transmitting cable connecting the sensor element to the electronic unit, a flexible tube having the cable and the sensor element disposed therein, a solid metal wire, and a coil attached to the distal end of the solid wire. The sensor element comprises a pressure sensitive device, e.g. a membrane, with piezoresistive elements connected in a Wheatstone bridge-type of arrangement mounted thereon.
As is recognized in U.S. Pat. Nos. 6,112,598 and 6,167,763, which also are assigned to the present assignee, a potential problem with this kind of guide wire mounted sensor is the occurrence of so-called bending artefacts. A bending artefact is a change in the output signal from the sensor that is induced by a bending of the guide wire, rather than being induced by a change in the physical environment surrounding the sensor. For a sensor and guide wire assembly like the one disclosed in U.S. Pat. No. Re. 35,648, this means that when the guide wire is bent, the bending of the guide wire imposes a strain on the sensor element, which thereby is deflected or stretched (or contracted). The deflection of the sensor element is then transferred to a deformation of the pressure sensitive device; and, according to well-known principles, the output from the Wheatstone bridge will thereby be affected by the bending of the guide wire.
According to U.S. Pat. Nos. 6,112,598 and 6,167,763, a solution to this problem is to mount the sensor element in a cantilevering fashion such that the pressure sensitive end of the sensor element does not contact any structure other than its mount. These two patents disclose several embodiments with different ways of mounting the sensor element such that bending forces are not exerted on the pressure sensitive end of the sensor element. A common feature of these embodiments is that an elongated, essentially rectangular sensor chip is mounted in a recess in the core wire in such a way that the proximal end of the chip is attached to the core wire, while the distal end of the sensor chip protrudes into the recess such that a clearance is provided below the distal portion of the chip where the pressure sensitive device (e.g. a membrane) is provided.
In the U.S. patent application Ser. No. 10/611,661, which is assigned to the present assignee, a clearance is also provided below the distal portion of the sensor chip, but here the chip has been provided with an extra mounting base, which at a proximal portion of the sensor chip protrudes downwards for mounting to the core wire and which thereby creates a clearance below a distal portion of the chip.
A principally different solution to the bending artefact problem is presented in the U.S. patent application Ser. No. 10/622,136, which also is assigned to the present assignee. Here the sensor chip is provided with a recess, which will act as a hinge or articulation when the core wire is bent. By the provision of this articulated portion, the pressure sensitive portion of the sensor element is not constrained to adapt to bending deformations of the core wire, which prevents such deformations from being transferred to the pressure sensitive device.
The entire contents of all of the above-described documents are incorporated herein by reference.
Although sensor and guide wire assemblies provided with sensor chips designed and mounted according to the different teachings of the above-listed documents in practise have proven to work well, the design of a sensor and guide wire assembly can be improved, not least from a manufacturing point of view.